During their different developmental stages, plants are exposed to an extremely wide range of biotic and abiotic stress conditions. The injury of crops as a result of abiotic and biotic stresses has been a major problem in the agricultural production areas. It is, thus, a very important task of high economic significance to develop new crops of simultaneously enhanced resistances against both abiotic and biotic stresses. Most functional genes have been limited on only one of those aspects. Recent trend is to find multifunctional genes that protect plant from both abiotic and biotic stresses. There are a few examples of multifunctional genes including “ferritin” gene that induces an enhanced resistance against a wide range of abiotic and biotic oxidative stress conditions (U.S. Pat. No. 6,563,019). However, there is almost no example of multifunctional gene that induces an enhanced resistance against abiotic and biotic stresses as well as an early flowering. All of those aspects are of significant factors in agricultural crop improvement.
There exists a continuing need to develop plants and crops that exhibit improved resistance to plant stresses, thereby increasing crop yields in adverse conditions and reducing the risk of crop failure. For example, plants with increased tolerance to drought, extreme temperatures and higher salt conditions may open the possibility of farming in semi-desert climates, where agriculture was previously non-viable. In addition, the development of novel crops with improved tolerance to cold or freezing temperatures may significantly prolong the growing season in regions with colder climates.
A number of plant genes are known to show increased levels of expression when plants are exposed to stress. However, despite considerable efforts to engineer genetically modified crops with increased stress tolerance, to date there are little or no such crops on the commercial market.
The future prospects of engineering novel plants with an increased capacity to tolerate environmental insults will depend on the modulation of critical stress tolerance controlling genes, and knowledge of their functional regulatory properties. The inventors for the present application, and others, have endeavored to decipher the mechanisms of plant stress tolerance in the hope of developing an understanding of the biochemical pathways involved. Nonetheless, the characterization of the genes and proteins involved in plant stress responses presents a number of significant challenges.
There remains a continuing need to develop a better understanding of plant stress responses, so that corresponding methods can be developed to confer advantageous properties to plants. This need extends to the production of crops that exhibit resistance to damage by adverse climatic conditions such as excessive temperatures, drought, and conditions of high salinity. Even incremental gains in plant stress tolerance may have a significant economic impact in stablizing the quality and supply of grain, oilseed and horticulture. Enhancement of germination, growth and flowering are extremely important in regions that have a short or otherwise difficult growing season.
In the Arabidopsis genome, there are two different groups of PLA2: 1) the secretory low molecular weight PLA2 (sPLA2) and 2) the patatin-like nonspecific PLAs which have combined PLA1 and PLA2 activities. Four low molecular weight PLA2 isoforms and 10 members of patatin-like PLAs have been found from the Arabidopsis genomic sequence database (Ryu et al., 2005 Progress in Lipid Research).
In order to identify multifunctional isoform(s) of PLA2, we have first focused on the four isoforms of sPLA2s, because the former are genuine PLA2s and are predicted to be secreted into endoplasmic reticulum and further into extracellular spaces and vacuoles. Endoplasmic reticulum and extracellular spaces have been proved to be key regulatory locations of multifunctional signaling in plants and animals. Among four isoforms of sPLA2, only sPLA2-a and sPLA2-b genes are expressed throughout whole plant tissues. On the other hand, sPLA2-e and sPLA2-g are found to be only expressed in flower tissues. The plant overexpressing a sPLA2-a or sPLA2-b protein exhibited an enhanced resistance against abiotic and biotic stresses. Interestingly, the transgenic plants overproducing sPLA-b protein also exhibited a phenotype of accelerated flowering time. Up to date, there is no report, to our best knowledge, that a gene simultaneously enhances three different aspects of agricultural traits such as resistance against both abiotic and biotic stresses as well as accelerated flowering time. It is noteworthy that a nonspecific patatin-like PLA has been found to be involved in the defense reaction of plants against attacks of pathogens (WO0183788).
In order to overcome above-mentioned problems of conventional methods, the present inventors have tried to develop plants and crops that exhibit improved resistance to plant stresses. Then, we have identified that commercially desired plants that have enhanced ability of flowering and more resistance against abiotic and biotic stresses can be produced by manipulating expression of sPLA2 gene in transgenic plants and completed the present invention successfully.
Throughtout this application, several patents and publications are referenced or cited in parentheses. The disclosure of these patents and publications is incorporated into this application in order to more fully describe this invention and the state of the art to which this invention pertains.